The manufacture of semiconductor devices often requires the formation of electrical conductors on semiconductor wafers. For example, electrically conductive leads on the wafer are often formed by electroplating (depositing) an electrically conductive layer such as copper on the wafer and into patterned trenches.
Electroplating involves making electrical contact with the wafer surface upon which the electrically conductive layer is to be deposited (hereinafter the “wafer plating surface”). Current is then passed through a plating solution (i.e. a solution containing ions of the element being deposited, for example a solution containing Cu2+) between an anode and the wafer plating surface (the wafer plating surface being the cathode). This causes an electrochemical reaction on the wafer plating surface which results in the deposition of the electrically conductive layer.
To minimize variations in characteristics of the devices formed on the wafer, it is important that the electrically conductive layer be deposited uniformly (with a uniform thickness) over the wafer plating surface. However, conventional electroplating processes produce nonuniformity in the deposited electrically conductive layer due to the “edge effect”. The edge effect is the tendency of the deposited electrically conductive layer to be thicker near the wafer edge than at the wafer center. Accordingly, improvements in methods of avoiding the edge effect continue to be sought.